Function

Engineers are often required to build on sites which consist of fine grained, saturated soils that have poor drainage properties. If the soil is not strengthened in advance, the added weight of a new structure will cause water to squeeze out over time. The soil layer will then compress or settle as water is removed. To prevent problems associated with excess settlement, it is important that excess pore pressures be removed from soft foundation soils within a short time frame. This is done with a prefabricated vertical drain.

PVDs, also known as Wick Drains, comprise of a synthetic drainage core wrapped with a durable fabric of excellent filtration properties. The vertical drain is designed to allow free flow of water in all directions and to ensure the integrity of the drainage system when subjected to tensile, compressive and buckling forces as the soft soil deforms and consolidates.

To prevent later problems of excess settlement, it is important that excess pore pressures be removed from soft foundation soils within a short time frame. This ensures that foundation shear strength is increased quickly to support embankment and fill loadings. However, soft compressible foundation soils have a low hydraulic conductivity and it takes a long time for excess pore pressures to dissipate and the soil to consolidate.

To reduce consolidation time, TenCate Alidrain prefabricated vertical drains (PVD) are installed to provide a shorter and easier drainage path for the pore water to drain. This speeds up consolidation and the soft foundation gains in shear strength quickly.

Applications

Alidrain Prefabricated Vertical Drains are ideal for soil consolidation in airport developments, road and rail embankments and in harbours.

Advantages

Once PVDs have been installed, fill is placed over the top of the site in order to generate excess pore pressures in the soft foundation soil. The excess pore pressure enables the pore water to drain out of the foundation soil and up the PVD where it is dissipated into a surface drainage blanket, beneath the placed fill. Once the desired consolidation has been achieved, construction continues.

A site can be completed in a number of months rather than a number of years if PVDs are not used.

Installation

During the consolidation process, lateral soil displacements can cause drains to elongate while vertical soil compression may cause drains to fold and buckle. Drain performance under both conditions must be considered when selecting a PVD as drain failure can jeopardise the construction schedule of the project and the stability of any structures built above it.

Our complete range of PVDs have been specifically designed to ensure that adequate drainage capability is maintained at all times, even under the most severe conditions

Our PVDs are available in a wide range of filter geotextiles and cores to suit various soil conditions and engineering practices.

The unique core has been specifically designed to ensure that adequate discharge capacity is maintained at all times, even under the most severe conditions.

Our team can assist with recommendation for the most appropriate PVD for your project.